1. Field of the Invention
The present invention relates to a capillary electrophoretic apparatus. More specifically, the invention relates to an electrophoretic apparatus that requires replacement or attachment of capillaries or a capillary array and that requires air to be removed out of a connecting section between the capillaries or the capillary array and the electrophoretic apparatus or out of passages that become electrophoretic passages.
2. Background Art
Capillary electrophoresis is now widespread as a technology for separating and analyzing many biological samples including deoxyribonucleic acid (DNA). One of technological advantages thereof is its excellent heat-radiating characteristic brought about by the surface-area to volume ratio of a capillary. This heat-radiating characteristic enables high-speed and high-resolution sample separation by electrophoresis using high voltage.
Capillary electrophoresis also has a feature that multiple analyses can be readily carried out using a large number of capillaries at the same time. A multiple-capillary type high-throughput electrophoretic apparatus has been put into practical use.
JP Patent Publication (Kokai) Nos. 2001-281221 A, 2001-324473 A, and 2001-324475 A disclose electrophoretic apparatuses using a capillary array composed of 16 capillaries.
A capillary is a fine tube having an inner diameter of several ten to several hundred microns. Its main material is quarts and polyimide of around several ten microns in thickness is coated around the outside of the quarts to enhance its mechanical strength. During electrophoresis, the capillary is filled with a component that becomes sample-separating medium.
Although non-fluid cross-linking polymer has been once used as the sample-separating medium, a non-cross-linking fluid polymer that excels in terms of productivity and performance stability is now the mainstream. JP Patent Publication (Kokai) No. 2001-281221 A discloses a pumping mechanism for filling gel, i.e., sample-separating medium, into capillaries. Although it discloses a glass syringe as the pumping mechanism, there also exists an electrophoretic apparatus that has a pumping mechanism for driving a sapphire plunger other than the glass syringe.
Furthermore, JP Patent Publication (Kokai) No. 2001-324473 A has disclosed a method of changing the length or number of capillaries corresponding to the type of analysis or a throughput required by a user. For example, relatively long capillaries are used in applications that require high resolution of distinguishing differences of length of one base of DNA from around several hundreds to thousand bases. Furthermore, relatively short capillaries are used when an analysis needs to be carried out quickly even if the resolution drops more or less. While a large-scale user such as a large-scale gene analysis center who handles a large number of samples at the same time requires a high throughput, a small-scale user on the level of laboratory often requires only a low throughput.
JP Patent Publication (Kokai) No. 2001-324475 A discloses a capillary array in a mode replaceable by the user. It is arranged so as to press down the capillary array at three points of a sample introducing end, an optical detecting section, and a polymer solution-supplying end. The polymer solution-supplying end of the capillary array is connected to a pumping mechanism of the electrophoretic apparatus.
More specifically, in the electrophoretic apparatuses disclosed in JP Application (Kokai) Nos. 2001-281221 A, 2001-324473 A, and 2001-324475 A, the polymer solution supplying end is arranged so that 16 capillaries are put into a bundle of around 3.5 mm in diameter that is inserted into an acrylic block in a horizontal direction and sealed and connected by a sleeve and a push screw. A syringe for a reservoir for storing polymer solution and an injection syringe for injecting the polymer solution into the capillaries at high pressure are attached to the block. The both syringes communicate with the capillary array via passages within the block. Furthermore, the electrophoretic apparatus has a second block to which a container for storing buffer solution can be attached. The first block to which the capillary array is attached is connected with the aforementioned second block by a tube. The capillary array communicates with the buffer solution provided in the second block through the passage formed in the first passage, the tube and a passage formed in the second block. An electrode that becomes an anode side is soaked into the buffer solution provided in the second block, so that the passage from the capillary array to the buffer solution becomes an electrophoretic passage to which voltage is applied during electrophoresis.
Because high voltage of several to several ten kilovolts is applied across the both ends of the electrophoretic passage in the electrophoretic apparatus, there is a possibility of causing discharge or the like if air is mixed into the electrophoretic passage. Because a section for connecting the capillary array with the electrophoretic apparatus is a part of the electrophoretic passage, bubbles must be reliably removed out of the connecting section in installing the capillary array to the electrophoretic apparatus.
In the apparatuses described above, the user removes the bubbles in installing the capillary array to the electrophoretic apparatus. The removal of the bubbles is normally carried out by moving a plunger of either glass syringe to supply the polymer solution to the passage and by discharging the bubbles together with the polymer solution out of a discharge port provided in the second block.
As a result of ardent study by the inventors of the present application, it was found that the ease of replacement of the capillary array is an important point when users evaluate controllability of the electrophoretic apparatus. The inventors also found that readiness of removal of air mixed in the passage in installing the capillary array largely influences the ease of replacement of the capillary array.
The diameter of the passages in the first and second blocks and the tube is as small as around 1 mm so that the removal of bubbles may be readily carried out. However, the larger the diameter of the capillary or the more the number of capillaries, the wider the space of the connecting section for connecting the capillary array with the electrophoretic apparatus becomes in order to accommodate the diameter (about 3.5 mm in case of 16 capillaries) of the bundle of the capillary array. The polymer solution flows from up to down in this part. The polymer solution flows in a direction opposite from a direction in which the bubbles within the polymer solution float up. Therefore, the solution flows locally within the space if the space of the connecting section is wide and the bubbles cannot be easily removed out just by moving the plunger to supply the polymer solution to the passage. There is even a case of consuming a large amount of valuable polymer solution due to the bubbles remaining in the capillary array connecting section.
In view of the problems described above, it is an object of the present invention to provide an electrophoretic apparatus that allows bubbles to be readily removed out of the electrophoretic passage.